Policy paper

Thames groundwater situation: 23 December 2024

Updated 23 December 2024

Applies to England

Current situation

Although groundwater levels are on a seasonal rising trend across the Thames catchment, rate of rise has declined and levels have broadly stabilised at some of the sites, due to the recent settled spell. Groundwater flood alerts have been issued at 2 locations, and a further 4 locations have reached levels that require early awareness.

Groundwater levels in the Lambourn Valley and Great Shefford areas, both in West Berkshire, have reached the levels that require groundwater flood alerts.

The levels at Hodcott (West Ilsley, East Ilsley, Compton, Chilton and West Hagbourne areas), Chapel Wood (Leckhampstead area), Water Acre (Upper Aldbourne Valley, Wiltshire) and Stonor (Henley and Assendon area, Oxfordshire) have also reached the levels that require early awareness. The levels at the Draycot Foliat in the Upper Og Valley have now dropped below the early awareness level.

This briefing note provides an update on the levels at these 6 locations. It also includes links to a range of websites containing further information.

Lambourn Valley

Groundwater levels at the Longacre observation borehole in the Lambourn Valley have stabilised. However, they remain at a level at which groundwater flooding may begin to affect communities. A groundwater flood alert was issued for this area on 10 December 2024. This will remain in force over the coming weeks as levels are expected to remain high and sensitive to further sustained periods of rainfall.

Great Shefford

Groundwater levels at the Northfield Farm observation borehole in the Great Shefford area remain high. Although the rate of rise has slowed slightly over the last few weeks, they have reached the level at which groundwater flooding may begin to affect communities. A groundwater flood alert was issued on 10 December 2024. This will remain in force over the coming weeks as levels are expected to remain high and sensitive to further sustained periods of rainfall.

West and East Ilsley, Compton, Chilton and West Hagbourne

Groundwater levels at our Hodcott observation borehole are above the level that requires early awareness and continue to rise. However, the rate of rise has slowed in the last week. Currently, no groundwater flood alert has been issued for this area but if the current increasing trend continues, we might issue one within the next few weeks. We will continue to monitor the situation closely and issue further briefing notes and alerts as and when needed.

Leckhampstead

Groundwater levels at our Chapel Wood observation borehole are above the level that requires early awareness and still rising, but the rate of rise has slowed in the last week. With the current rate of rise, we do not expect to issue a groundwater alert within the coming few weeks, but we will continue to monitor the situation closely and issue alerts as and when needed.

Upper Aldbourne Valley

Groundwater levels at our Water Acre observation borehole are above the level that requires early awareness but are currently stable. With the current rate of rise, we do not expect to issue a groundwater alert within the coming few weeks, but we will continue to monitor closely and issue alerts as and when needed.

Henley and Assendon

Groundwater levels at our Stonor observation borehole have reached the level that requires early awareness and are still rising slowly. With the current rate of rise, we do not expect to issue a groundwater alert within the next couple of weeks, but we will continue to monitor closely and issue alerts as and when needed.

Summary of other groundwater sites

Levels at our groundwater sites are generally higher than normal for the time of year and have responded to recent wet periods. Most have an increasing trend. This rising trend is expected to continue in response to the winter recharge. We continue to monitor groundwater levels and will update this briefing note and issue flood alerts as and when appropriate.

Forecast risk of flooding

The Met Office weather forecast indicates that the rest of December and early January could be broadly settled and drier than average.

The forecast is regularly updated and can be seen in the Met Office’s long range forecast.

More details can also be found in the monthly water situation report for England.

What we’re doing

We are:

• continuing to monitor groundwater levels across the area
• monitoring and clearing screens on main rivers in the area to ensure they flow freely
• talking with the local authority and other responding partners to ensure they are aware of the situation

Actions and advice

Call Floodline on 0345 988 118 or visit check for flooding on GOV.UK to find out if you can register to receive free flood alerts for flooding from groundwater.

You can monitor daily groundwater levels at the Longacre borehole at Groundwater level at Longacre.

You can monitor daily groundwater levels at the Hodcott borehole (West and East Illsley, Compton, Chilton and West Hagbourne) at Groundwater level at Hodcott.

You can monitor groundwater levels for the Northfield Farm observation borehole (Great Shefford) at Groundwater level at Northfield Farm.

You can monitor groundwater levels for the Chapel Wood observation boreholde (Leckhampstead) at Groundwater level at Chapel Wood.

You can monitor groundwater levels for the Water Acre observation borehole (Upper Aldbourne Valley, Wiltshire) at Groundwater level at Water Acre.

You can view historic levels for our sites on the Hydrology Data Explorer. This includes Draycot Foliat.

Check the river, sea, groundwater and rainfall levels on GOV.UK.

You should:

• review your individual and community group flood plans
• check pumps and any other flood protection equipment you have
• keep drains and gullies around your property free of debris
• move valuables from basements and cellars

Next update

Flood risk increases with the continuing rising groundwater. We will update this briefing note weekly for as long as one or more sites exceed the notification levels. We will also issue updates if the situation changes significantly.

Further information

See more information on groundwater levels and the water situation report.

You can also get practical advice on what to do before, during and after groundwater flooding and see the flood forecast for the next 5 days. Visit check for flooding in England.

Contacts

For more information on the flood alert service and to find out what messages you are registered to receive, call Floodline on 0345 988 118.

Alternatively, you can contact the Environment Agency for more information:

• customers and engagement: [email protected]
• national customer contact centre: 03708 506 506
• incident reporting hotline: 0800 807 060